This invention relates to engraving heads of the general type disclosed in Buechler U.S. Pat. No. 4,450,486. Such engraving heads comprise a diamond stylus carried by a holder mounted on an arm projecting from a torsionally oscillated shaft. A sine wave driving signal is applied to a pair of opposed electromagnets to rotate the shaft through a maximum arc of approximately 0.25xc2x0 at a frequency in the neighborhood of about 3,000 to 5,000 Hz.
A guide shoe is mounted on the engraving head in a precisely known position relative to the oscillating stylus. The engraving head is supported for tilting movement by a set of leaf springs secured to a rearwardly projecting bar. A DC motor rotates the bar so as to bring the guide shoe into contact with a printing cylinder to be engraved. When the guide shoe is in contact with the printing cylinder, the stylus oscillates from a position just barely touching the printing cylinder to a retracted position about 100 microns distant from the surface of the cylinder.
Once the guide shoe is in contact against the printing cylinder a video signal is added to the sine wave driving signal for urging the oscillating stylus into contact with the printing cylinder thereby engraving a series of controlled depth cells in the surface thereof. The printing cylinder rotates in synchronism with the oscillating movement of the stylus while a lead screw arrangement produces axial movement of the engraving head so that the engraving head comes into engraving contact with the entire printing surface of the printing cylinder.
In engraving systems of the type taught by Buechler, it is necessary for the machine operator to perform a tedious trial and error setup procedure at one end of the printing cylinder prior to commencement of engraving. This procedure involves adjustment of the gain on amplifiers for the sine wave driving signal and the video signal so as to produce xe2x80x9cblackxe2x80x9d printing cells of a desired depth together with connecting channels of another desired depth and clean non-engraved white cells or areas. Each change of one of the control variables interacts with the others, and therefore the setup becomes an iterative process.
There is also a need in the engraving industry to provide an engraving system and apparatus with imaging and focusing capabilities which further facilitate automatically focusing on a surface of the cylinder and subsequently capturing images and measuring engraved areas on the surface. What is also needed is an engraving system which can quickly measure a dimension of a cut or cell, for example, of precisely controlled dimensions during set-up or real-time operation of the engraver.
There is a further need to provide a system and method for processing data corresponding to captured images, for example, by eliminating undesired image data or filling in discontinuous data corresponding to gaps in the array of data which correspond to gaps in a captured image.
What is also needed is an engraver comprising an apparatus or method for scaling or calibrating the intensity of light used in the focusing process to enhance automatically focusing, measuring and engraving cuts of precisely controlled dimensions.
It is therefore seen that a need has existed for an engraving system which may be quickly and easily set up to engrave cells of precisely controlled dimensions in the surface of a gravure printing cylinder.
In one aspect, this invention comprises a method for adjusting an engraver to engrave a cylinder with an actual cut according to predetermined setup parameters, said method comprising the steps of: (a) determining an error value corresponding to the difference between said predetermined setup parameters and an actual measurement of a portion of an engraved area on said cylinder; and (b) using said error value to adjust said engraver to engrave said actual cut in accordance with said predetermined setup parameters.
In another aspect, this invention comprises a method for measuring a portion of an engraved area on a cylinder in an engraver, said method comprising the step of generating a plurality of actual dimension values corresponding to said portion.
In still another aspect, this invention comprises a system for measuring a portion of an engraved area on a cylinder in an engraver, said system comprising a measuring device for generating a plurality of actual dimension values corresponding to said portion.
In yet another aspect, this invention comprises an error correction system for use in an engraver suitable for engraving a cylinder with an actual cut in accordance with predetermined setup parameters, said error correction system comprising determining means for determining an error value corresponding to the difference between the predetermined setup parameters and a measurement of the actual dimensions of a portion of an engraved area on said cylinder; and a system coupled to said determining means for receiving said error value and also for adjusting said engraver to engrave said actual cut in accordance with said predetermined setup parameters.
In still another aspect, this invention comprises a method for measuring a portion of a cylinder in an engraver, the method consists of the steps of focusing on a focus area of cylinder with an imager, imaging the portion with the imager, generating an array of data corresponding to the portion, and determining at least one actual dimension value using the array of data.
In another aspect, this invention comprises a system for imaging an area of a cylinder in an engraver, the system comprising an imager for capturing an image of the engraved area and a video processor coupled to the imager for generating a plurality of dimension values corresponding to the image, the imager comprising an illuminator capable of illuminating the area to a plurality of light intensity levels.
In another aspect, this invention comprises an engraver for engraving a plurality of cells on a surface of a cylinder engraver consisting of a support for rotatably supporting the cylinder, an engraving head for engraving the cylinder, the engraving head being mounted in operable relationship with the cylinder when the cylinder is rotatably mounted on the cylinder, and an image system associated with the engraving head for capturing an image of an area on the surface.
In a still further embodiment, a method for imaging an area of a surface of a cylinder comprises the steps of supporting the cylinder on an engraver in operative relationship with an engraving head, imaging the area of the cylinder with an imager associated with the engraving head to provide image data, and focusing the imager on a surface of the cylinder using the image data.
The present invention also provides an engraving apparatus and method wherein a plurality of parameter signals are supplied to a setup circuit or computer for computing engraving parameters to control the engraving response of the engraving stylus to an input video signal. An input AC signal and an input video signal are multiplied by multiplication factors which are generated by the computer. The computer also generates a white offset signal which is combined with the above mentioned multiplication factors to produce a driving signal for the engraving stylus. The stylus then engraves cells of the desired geometry.
The computer is provided with input signals which indicate a desired black cell width, a desired channel width, a desired highlight cell width and the video voltage level at which a highlight cell of the desired width is to be engraved. The values of these parameters are used for solving a set of equations which produce the appropriate values for the two multiplication factors and the white offset.
A video camera is operated to produce a frame of video information including an image of an engraved area, such as a cell, which has been engraved by a video signal of a predetermined level. A video processing circuit measures the width of the cell which has been so imaged and reports it to the computer. The computer then adjusts the multiplication factors and the white offset through use of an error term which is equal to the difference between the expected cell width and the measured cell width.